1. Field of the Invention
The present invention relates generally to rotation-angle detection devices and methods and image processing apparatuses and, more particularly, to rotation-angle detection devices and methods and image processing apparatuses configured to detect a rotation angle of a rotor accurately with an inexpensive structure.
2. Description of the Related Art
In image processing apparatuses such as printers, facsimiles, copiers, scanners, and multifunction peripherals (MFPs), drive mechanism is driven by drive motor to thereby drive each element involved in image processing, such as an image reading operation or an image forming operation, at a predetermined speed.
In a conventional technique for rotating a rotor such as a drive motor at a desired rotation speed, a rotation angle of the rotor on which a permanent magnet is arranged is detected as follows. A magnetic sensor, the output signal of which sinusoidally varies with the rotation angle of the rotor is arranged near an outer circumference of the rotor. A rotation-angle detection device detects the rotation angle of the rotor based on the output signal of the magnetic sensor. More specifically, a magnetic sensor such as a Hall element is used as the magnetic sensor. The rotation-angle detection device detects the rotation angle of the rotor based on the output signal of the magnetic sensor using a sequential search algorithm.
A conventional technique to this end is disclosed in Japanese Laid-open Patent Application No. 2010-217150 as an angle detection device which receives output signals from at least one pair of Hall elements, each pair of which is arranged perpendicular to each other, and obtains a detected rotation angle of a value which depends on an angular displacement from a reference position in a magnetic field. The angle detection device includes: a ΔΣ modulation unit which performs ΔΣ modulation of the output signals of the Hall elements based on a reference signal; a gain control loop which controls the reference signal fed to the ΔΣ modulation unit so that a root sum square of signals output from the ΔΣ modulation falls within a predetermined range; a storage unit which stores sine function values and cosine function values of plural angles; an angle detection loop which controls a sine function value and a cosine function value of a specified angle output from the storage unit so as to zero an angle error signal calculated from the signals output from the ΔΣ modulation unit and the sine function value and the cosine function value, and obtains a detected angle output based on the sine function value and the cosine function value.
This conventional technique is aimed at making highly-accurate angle detection possible while allowing flexible arrangement of the magnets and the Hall elements by configuring the angle detection device to include the ΔΣ modulation unit, the gain control loop, the storage unit, and the angle detection loop. The angle detection loop controls a sine function value and a cosine function value of a specified angle so as to zero an angle error signal which is calculated from a result of ΔΣ modulation of output signals of the Hall elements based on a gain-controlled reference signal, and the sine function value and the cosine function value, and obtains a detected angle output based on the controlled sine function value and cosine function value.
However, the conventional technique disclosed in Japanese Laid-open Patent Application No. 2010-217150 is disadvantageous in that building the angle detection device including the ΔΣ modulation unit, the gain control loop, the storage unit, and the angle detection loop is expensive.
Under the circumstances, there is a need to provide a technique for detecting a rotation angle of a rotor accurately with an inexpensive structure.
It is an object of the present invention to at least partially solve the problem in the conventional technology.